Valves typically comprise a valve housing having a fluid passage and a valve member movable from an open position permitting flow through the passage to a closed position in which flow is shut-off. In the closed position contacting surfaces on the valve housing and the movable valve member provide a substantially fluid tight seal to assure that all fluid flow is shut-off.
Valves formed of cast or nodular iron are conventionally constructed with at least one of the contacting elements formed of metal and provided with a smooth or fine finish surface. The other of the surfaces may be formed by a resilient sealing member or another machined metal surface. Such machined surface may be metal member having a fine finish and welded to the valve.
A smooth or fine finish is important when a resilient member is provided on the other surface. Failure to provide a smooth metal surface will cause excessive wear or damage to the resilient member during opening and closing so that the useful life of the seal is materially reduced.
Heretofore, valves made from cast or nodular iron have often been constructed with one of the sealing surfaces provided on a separate metallic member having a machined or ground surface and fixed to the valve part mechanically or by welding. This separable structure not only increases the cost of the valve but is also susceptible to undesirable cracking of the cast valve part to which the member is welded. Moreover, the heat generated during welding may cause carbon and impurities from the cast iron to comingle or contaminate the weld attaching the non-corrosive member so that the corrosion resistant characteristics of the welded assembly are reduced thereby decreasing its durability.
The bonded seated surface does not contain crevices characteristic of a mechanically attached separate member which provides a site for corrosive action to occur.
By the present invention it is proposed to provide a valve having a new and improved sealing structure which overcomes the difficulties encountered heretofore.
This is accomplished generally by a valve including a valve body having a fluid passage. A valve member is mounted within the fluid passage for movement allowing the flow of fluid through the passage to a closed position for sealing the passage and preventing flow therethrough. The seal is defined by mating or contacting surfaces provided on the valve body wall defining the passage and the peripheral of the valve member. At least one of the mating surfaces is formed with a bonded overlay composition having a wear resistant, non-corrosive surface capable of being polished to a high finish.
One such composition suitable as a bonded coating is a non-exothermic nickel-chromium powder alloy, for example containing by weight about 18 to 22.5% of chromium and about 68.5 to 72.5% of nickel with the remaining elements including carbon, manganese, silicon and iron.